One of the ruffians heard the snapping crunch, and uttered a cry of amazement.

The cry was echoed by hurried footsteps in the house.

Then a rear door was suddenly thrown open by Rufus Venner, and a flood of light revealed the struggling men, still battling furiously on the pavement.

Nick now had both opponents down, and within another minute he would have had them at his mercy, a fact which Venner instantly perceived.

He sprang nearer, drew his revolver, and dealt the detective a single swinging blow upon the head.

Nick dropped like an ox struck down in the shambles.

The darkness of night was as nothing to the darkness that instantly fell upon him.

CHAPTER VII

A strategic move.

Nick Carter had a head that was used to hard knocks, and it required more than one to put him down and out for any considerable period.

The great detective recovered consciousness within half an hour after the blow received from Rufus Venner, and he fell to taking the measure of his situation the moment the cobwebs began to clear from his brain.

He found himself bound hand and foot with ropes, and lying upon the floor of a dark room.  That he was in the dwelling occupied by the Spanish dancer, Nick had not a doubt.

As his mind became clearer and his eyes accustomed to the darkness, Nick discovered a narrow thread of light some yards away and close to the floor, and presently the sound of lowered voices faintly reached his ears.

“A light in the next room,” he said to himself.  “Probably the whole gang is out there, sizing up my case, and deciding what to do with me.  If they are there, I must get a better look at those two ruffians.  I owe them something for their work of to-night, and I always mean to pay such debts.

“One of them was called Dave, and it may have been Dave Kilgore himself.  In which case, by Jove!  I was right in thinking that this diamond robbery only masks some deeper and bigger game.

“I wonder if they suspect my identity.  If not, what sort of a game have they been playing here to-night?”

Nick very quickly measured the various possibilities of the unusual situation.

If the man whose name he had heard was indeed David Kilgore, then Rufus Venner, as well as Cervera, might be in league with the diamond gang, and the pretended robbery only a move made with some secret design.

On the other hand, Venner might be entirely ignorant of Kilgore’s identity, and without any serious suspicions of Cervera, being himself a blind victim of these notorious criminals.

“If the latter is the case,” reasoned Nick, “the gang may stand in fear of me, and perhaps are afraid that I shall foil some scheme they have in operation, or are about to undertake.  Then they to-night may have aimed only to discover the extent and nature of my suspicions.